This invention is concerned with articulated vehicles and, more particularly, with means for coupling the front and rear bogies of such vehicles and for steering them. The invention is particularly adaptable to self-propelled agricultural machines such as combine harvesters.
Hinge-steer articulated vehicles are, potentially, more stable on side slopes than rigid chassis vehicles of similar dimensions. The necessary oscillation (about a longitudinal axis) between front and rear portions or bogies of the vehicle is provided for in the connection between them. However, when steering is by mechanical linkage connected between the bogies, it is desirable to "isolate" the linkage so that oscillation does not influence the steering. A common method for achieving this isolation is illustrated in U.S. Pat. Nos. 4,181,315 van der Lely and 4,317,326 Riedinger (also assigned to the assignee of the present invention). Both disclose similar mechanisms the first in a tractor, the second in a combine harvester. In the tractor, a swivel in tandem with the steering linkage permits oscillation without affecting (twisting) the steering linkage. Disadvantages of this system include having to accommodate the lengthy tandem combination of steering linkage and swivel and the relatively high cost (including machining cost) and weight of the parts involved. The combine arrangement is more compact but the other disadvantages remain.